The present invention relates to a liquid crystal composition comprising a mesogen containing compound and a compound selected from a photochromic compound, a dichroic compound and a photochromic-dichroic compound, formulations thereof, optical elements, liquid crystal polymers comprising same and methods of making same.
The molecules of a liquid crystal (“LC”) tend to align with one another in a preferred direction, yielding a fluid material with anisotropic optical, electromagnetic, and mechanical properties. The mesogen is the fundamental unit of a LC which induces the structural order in the liquid crystals.
Liquid crystal polymers (“LCPs”) are polymers capable of forming regions of highly ordered structure while in a liquid phase. LCPs have a wide range of uses, ranging from strong engineering plastics to delicate gels for LC displays. The structure of LCPs may consist of densely packed fibrous polymer chains that provide self-reinforcement almost to the melting point of the polymer.
Dichroism may occur in LCs due to either the optical anisotropy of the molecular structure or the presence of impurities or the presence of dichroic dyes. As used herein, the term “dichroism”, means the ability to absorb one of two orthogonal plane polarized components of at least transmitted radiation more strongly than the other.
Conventional, linearly polarizing elements, such as linearly polarizing lenses for sunglasses and linearly polarizing filters, are typically formed from stretched polymer sheets containing a dichroic material, such as a dichroic dye. Consequently, conventional linearly polarizing elements are static elements having a single, linearly polarizing state. Accordingly, when a conventional linearly polarizing element is exposed to either randomly polarized radiation or reflected radiation of the appropriate wavelength, some percentage of the radiation transmitted through the element will be linearly polarized. As used herein the term “linearly polarize” means to confine the vibrations of the electric vector of light waves to one direction or plane.
Further, conventional linearly polarizing elements are typically tinted. That is, conventional linearly polarizing elements contain a coloring agent (i.e., the dichroic material) and have an absorption spectrum that does not vary in response to actinic radiation. As used herein “actinic radiation” means electromagnetic radiation, such to ultraviolet and visible radiation that is capable of causing a response. The color of the conventional linearly polarizing element will depend upon the coloring agent used to form the element, and most commonly, is a neutral color (for example, brown or gray). Thus, while conventional linearly polarizing elements are useful in reducing reflected light glare, because of their tint, they are not well suited for use under certain low-light conditions. Further, because conventional linearly polarizing elements have only a single, tinted linearly polarizing state, they are limited in their ability to store or display information.
As discussed above, conventional linearly polarizing elements are typically formed using sheets of stretched polymer films containing a dichroic material. As used herein the term “dichroic” means capable of absorbing one of two orthogonal plane polarized components of at least transmitted radiation more strongly than the other. Thus, while dichroic materials are capable of preferentially absorbing one of two orthogonal plane polarized components of transmitted radiation, if the molecules of the dichroic material are not suitably positioned or arranged, no net linear polarization of transmitted radiation will be achieved. That is, due to the random positioning of the molecules of the dichroic material, selective absorption by the individual molecules will cancel each other such that no net or overall linear polarizing effect is achieved. Thus, it is generally necessary to suitably position or arrange the molecules of the dichroic material by alignment with another material in order to achieve a net linear polarization.
In contrast to the dichroic elements discussed above, conventional photochromic elements, such as photochromic lenses that are formed using conventional thermally reversible photochromic materials, are generally capable of converting from a first state, for example, a “clear state,” to a second state, for example, a “colored state,” in response to actinic radiation, and then reverting back to the first state in response to thermal energy. As used herein, the term “photochromic” means having an absorption spectrum for at least visible radiation that varies in response to at least actinic radiation. Thus, conventional photochromic elements are generally well suited for use in both low-light conditions and bright conditions. However, conventional photochromic elements that do not include linearly polarizing filters are generally not adapted to linearly polarize radiation. That is, the absorption ratio of conventional photochromic elements, in either state, is generally less than two. As used herein, the term “absorption ratio” refers to the ratio of absorbance of radiation linearly polarized in a first plane to the absorbance of the same wavelength radiation linearly polarized in a plane orthogonal to the first plane, wherein the first plane is taken as the plane with the highest absorbance. Therefore, conventional photochromic elements cannot reduce reflected light glare to the same extent as conventional linearly polarizing elements. Thus, photochromic-dichroic materials have been developed. Photochromic-dichroic materials are materials that display photochromic properties (i.e., having an absorption spectrum for at least visible radiation that varies in response to at least actinic radiation) and dichroic properties (i.e., capable of absorbing one of two orthogonal plane polarized components of at least transmitted radiation more strongly than the other).
Photochromic materials and photochromic-dichroic materials may be incorporated into a substrate or an organic material, for example a polymer substrate, including LCP substrates. When photochromic materials and photochromic-dichroic materials undergo a change from one state to another, the molecule(s) of the photochromic compound or photochromic-dichroic compound may undergo a conformational change from one conformational state to a second conformational state. This conformational change may result in a change in the amount of space that the compound occupies. However, for certain photochromic materials and certain photochromic-dichroic materials to effectively transition from one state to another, for example to transition from a clear state to a colored state, to transition from a colored state to a clear state, to transition from a non-polarized state to a polarized state, and/or to transition from a polarized state to a non-polarized state, the photochromic compound or photochromic-dichroic compound must be in an chemical environment that is sufficiently flexible to allow the compound to transition from one conformational state to the second conformational state at a rate that is sufficient to provide the desired response on over an acceptable time frame. Therefore, new polymeric materials, such as new LCPs, and materials to form these new materials are necessary to further develop photochromic and photochromic-dichroic materials and substrates.